1. Field of the Invention
This invention is concerned with septic drainfields for the treatment of liquid effluent discharged from septic tanks handling household sewage. More specifically, this invention relates to drainfields constructed in multi-level layers.
2. Description of the Prior Art
Current prior art practice is illustrated in FIG. 1 of the accompanying drawings, wherein sewage from house H is delivered to underground septic tank S and separated, with the aid of baffles B and gravity, into supernatant scum, sludge settled to the tank bottom, and liquid effluent, which emerges from tank S and is carried through distribution box C and pumped through perforated distribution pipe P, to be spread on soil absorption bed or drainfield D. The drainfield acts as a filtration medium for the liquid effluent, removing suspended matter therefrom; the drainfield also serves as a chemical reaction medium wherein the degradation and oxidation of noxious or unpleasant compounds in the effluent occurs; most importantly, the drainfield provides a culture medium for soil bacteria, which flourish and form a slime coating the particles of the soil absorption bed. The drainfield thereby becomes a deathtrap to dangerous health-imperiling viruses, which are removed from the effluent by being either held in the bacterial slime or trapped on the soil particles' surfaces, long enough for the viruses to be digested by the bacteria or to be neutralized and rendered harmless. Thereby, the treated liquid effluent may pass safely from the drainfield into the surrounding soil and eventually join the surrounding ground water without contaminating nearby wells or streams.
The requirements for successful and safe conventional drainfield operation are rigidly controlled by local and state health authorities to prevent the spread of infectious diseases by water supply contamination. These requirements include: 1) a drainfield area large enough to accommodate safely the maximum volume of sewage effluent generated by the household involved; 2) a drainfield soil with a pore size and structure such that the liquid effluent will percolate therethrough at a filtration rate in the range of but not exceeding one inch per hour; 3) a drainfield thickness of at least four and one-half feet, situated above the seasonal high groundwater table; and 4) a drainfield not in low areas where rain or snow accumulation can overflow the system, and not on steep slopes.
Many potential homesites in non-sewer areas cannot meet the above drainfield requirements because of inadequate soil characteristics or unsatisfactory available area or location therefor, and thus cannot be developed with conventional sewage disposal methods without major land reconfiguration and major expense. Even for existing drainfields, which require consistent maintenance and eventual digging out and replacement when they become saturated and spent, costs can run prohibitively high.